I have Ubuntu 10.12 32 Bit installed. As you already should know, the newest beta 12.11 (that is version 8 of the 12.11) on the amd website is not working with steam, because it causes a crash. You need to install the 12.11 beta 1 driver. Afterwards I had 30 - 140 fps. For me it was perfectly playable. FPS never fallen under 30 FPS. (Optimized Settings, set something to medium, just ask for my settings if your interested in) before it was too laggy to have fun. Played several hours yesterday with 26 People ^^. I am using an Intel E7400 (2x 2,8 GHz), 6 GB RAM and an ATI Radeon HD 6850 with Display Resolution 1920 x 1080. So you need this driver: http://www2.ati.com/drivers/beta/amd-driver-installer-catalyst-12.11-beta-x86.x86_64.zip

Note: For 64 Bit and 32 Bit Versions of Linux there are 2 different ways to remove the amd watermark. Just google and you will find both ;)

When I launch TF2, it has a black screen, but I have found if I press "ctrl+alt+f1" then "ctrl+alt+f7" when I hear the audio from the intro video, I the screen starts working again. I'm not sure why it does this, but it seems to help with almost all graphical problems I've been having with the AMD proprietry drivers.